1. Field of the Invention
The present invention is concerned with an improved crop drying system and method, and with a preferred predrying apparatus for use in the overall system. More particularly, it is concerned with such a system which preferably includes a conventional rotary kiln primary dryer along with an indirect heat exchange predryer and structure operatively coupling the dryers such that the waste heat from the primary dryer is employed in the predryer. In this fashion heat utilization is increased with a concomitant decrease in fuel costs, drying capacity is increased as compared with the single rotary dryer, and atmospheric pollution is measurably lessened.
2. Description of the Prior Art
Direct fired rotary kiln drum dryers are conventionally used for drying a variety of crops such as alfalfa and the like. In such units, hot air heated from a furnace or burner is directed to the elongated, axially rotating drum along with crop to be dried. The dried crop and hot, moist air are discharged from the dryer and are separated, usually by means of a cyclone separator. In this conventional arrangement, the hot, moist air from the dryer outlet is simply discharged to the atmosphere. This practice is extremely wasteful in terms of energy usage, particularly when it is appreciated that in many cases a high percentage (e.g., approximately 80 percent) of the total heat expended by the dryer is available for drying purposes. In short, the conventional practice is relatively inefficient in terms of energy usage.
Moreover, drying operations of the conventional variety are troublesome in that large quantities of particulate material can be discharged into the atmosphere. This problem has led to the promulgation of a plethora of rules and regulations regarding particulate discharge from such installations. This has in turn forced many operators to install expensive supplemental equipment in an attempt to alleviate the pollution problem.